Cellular phones have been widely used through out the world. Further, there is no end for such booming because among other advantageous benefits as compared to conventional wire telephone, cellular phone is slim, multifunctional, inexpensive, portable, and convenient while still maintaining a high communication quality. Hence, more and more people like to use cellular phones whether for business or social purpose. But the capacity of a rechargeable battery of cellular phone is relatively small. Hence, cellular phone is off when battery is too low. As a result, a user having a disconnected cellular phone may miss important calls even the calling party can leave a message/telephone number in a memory (e.g., voice box) of cellular phone of the called party during this off period. Hence, there is a need to provide an effective power saving method so as to increase the service time per full charge of cellular phone.